Unraveling dark Higgs mechanism via dark photon production at an e^+ e^- collider

TL;DR

The paper addresses how a light dark Higgs arising from a dark $U(1)'$ Higgs mechanism can affect collider searches for invisible dark photons. It develops a dark-FSR framework with a dark shower and a merging scheme to accurately describe $e^+e^-\to \gamma A'$ plus $A'\to$ invisible, including the case where $A'\to A's$ radiation is collinear. Applying this to BaBar, the authors recast the invisible DP search, showing that dark FSR modestly enhances the cross section and broadens the missing-mass distribution, yielding a slightly stronger exclusion on the kinetic mixing $\varepsilon$ with a typical shift of a few percent and a systematic uncertainty up to $\sim3.4\%$. The work provides a practical pipeline for incorporating dark-sector radiation into collider constraints and demonstrates its impact on current and future searches.

Abstract

In the phenomenology study of dark photon, its mass origin is usually not under concern. However, in theory construction its mass is often generated via a dark Higgs mechanism, which leads to the presence of a light (non-decoupled) dark Higgs particle. In this work, we study the impact of such a dark Higgs particle in the collider detection of the dark photon. We focus on the process of final state dark photon radiating dark Higgs, which is called dark final state radiation (FSR). Considering the effects on both the signal cross section and the distribution of the missing mass square, the invisible dark photon search at BaBar is reanalyzed and a new exclusion limit for invisible dark photon is presented.

Figures (9)

• Figure 1: Illustration for the method to deal with the dark FSR.
• Figure 2: The probability for a final-state DP to radiate $N_s$ dark Higgs bosons given by the parton shower simulation. Solid, dashed and dash-dotted curves correspond to $\alpha' = 0.5$, $0.3$ and $0.1$, respectively. Red, blue and green curves represent $N_s = 1$, $2$ and $3$, respectively.
• Figure 3: The tree-level cross sections (with $p^T_{\gamma}>1$ GeV) and their ratio as functions of $m = m_{A'} = m_{s}$. The solid and dash-dotted blue lines are the cross sections for the $e^+ e^- \to \gamma A' s$ and $e^+ e^- \to \gamma A'$ processes, respectively, while the red line shows their ratio.
• Figure 4: The $\Delta R$ distributions and a schematic illustration of the merging procedure. The orange line represents the hard scattering process $e^+ e^- \to \gamma A' s$. The blue histogram is filled with showered events of $e^+ e^- \to \gamma A'$ with at least one dark Higgs boson in the final state. And both are normalized to the ratio of their respective cross sections to $\sigma_\text{ME}(e^+ e^- \to \gamma A')$. The green shaded region represents the distribution after merging.
• Figure 5: The signal cross sections as functions of $m = m_{A'} = m_{s}$. The black dashed curve represents the cross section incorporating dark FSR. The solid and dash-dotted blue lines are for the components without or with dark Higgs bosons in final state, respectively. The red line represents the correction factor $S_{\text{cxs}} \equiv \sigma_{\text{no-FSR}} / \sigma_{\text{tot}}$ introduced to $\varepsilon^2$ due to the cross section variation.